In the production of viscous hydrocarbon such as heavy crude and bitumen from tar sands, it is necessary to thoroughly stimulate the viscous material by lessening its viscosity to flowable condition. Thus, the bitumen, in emulsion form, can flow or be withdrawn from the substrate.
Usually thermal stimulation comprises the introduction of a pressurized flow of a heating medium such as steam into the substrate by way of an injection well. In the instance of tar sands, this step, over a period of time, liquefies the bitumen and releases it from its retained condition in the tar sand and causes formation of a mixture with condensate. The steam also establishes a pressure front whereby to urge the now flowable hydrocarbon mixture toward one or more spaced apart production wells.
Although the hereinafter described method and apparatus can be applied to the production of either bitumen or heavy crude oil, the following disclosure will define the invention in terms of the production of bitumen from a tar sand environment.
A preferred method adapted to viscous hydrocarbon production utilizes a single well which is sequentially heated, and produced to operate on a cyclical principle. More specifically, the substrate surrounding the well is initially preheated under pressure to convert bitumen into flowable condition.
Thereafter, during a soak period, steam is condensed, and heat is absorbed into the substrate thereby causing the bitumen emulsion or mixture to gravitate toward the lower pressure well and be produced therefrom.
When, over a period of time, ambient pressure within the substrate becomes depressed, it is necessary to recommence the cycle by the further introduction of a stimulating medium. As a sufficiently high heat and pressure environment is reestablished and bitumen emulsion is again caused to flow, steam injection is discontinued or minimized. Further controlled draining of bitumen emulsion can now be resumed.
This cyclical process can be repeated indefinitely until the area adjacent to the well becomes exhausted of hydrocarbon product. The method is generally referred to as the huff and puff process. It is found to function effectively particularly when the stimulating medium is steam.
In an alternate method of producing hydrocarbons from a substrate, a plurality of vertical walls are drilled in a desired pattern. Thereafter, the stimulating fluid such as steam, under pressure, is injected for a period of time into the substrate by way of a centrally located injector well.
The heated or stimulated area about the well will gradually be widened, thereby establishing an expanding pressure front. The latter urges flowable bitumen emulsion toward the surrounding producing wells. This process is advantageous in that it can be practiced by a continuous, rather than a cyclical introduction of stimulating fluid.
Tar and deposits generally occur in horizontal layers. It has been found desirable therefore, toward achieving an improved hydrocarbon production rate, to utilize a generally horizontally disposed well for producing from the layer. However, the nature of the horizontal well mandates that the latter operate on a cyclical basis to realize an appreciable outflow of bitumen emulsion. Since this cyclical operation amounts to disruption of the producing phase, it constitutes a less than desirable expedient.
To increase the rate of production from a horizontal well of the type contemplated, there is presently provided an efficient method and apparatus for establishing a flowable bitumen emulsion in and through a tar sand environment. The process is effectuated through use of an elongated, horizontal well which traverses at least a portion of the tar sands layer.
A vertical well is positioned to intersect or terminate in the region of the horizontal well and serves to facilitate the producing process as well as to provide communication with the horizontal well.
Operationally, both the horizontal well and the adjacent substrate are initially preheated to establish a favorable operating temperature at which fluidized bitumen emulsion can flow. The horizontal well liner embodies a liner which includes longitudinally adjustable means or barrier therein, to outwardly divert the stimulating steam. The fluid thereby creates a hot path along which subsequent bitumen emulsion flows. Said hot path communicates the relatively high pressurized injection area where the stimulating fluid is introduced, with a lower pressure area through which production takes place.
Thereafter, and subsequent to the preheating step, the well is produced by the controlled introduction of a stimulating fluid as needed. This latter introduction, together with regulation of the well back pressure, causes fluidized bitumen emulsion to be urged to the well producing end.
As one area of the adjacent substrate becomes depleted, the steam flow is altered to establish new paths by adjusting the location of the steam diverting barrier horizontally along the well liner.
It is therefore an object of the invention to provide the method and apparatus for improving production output of a viscous hydrocarbon fluid from a subterranean reservoir in which the fluid is locked. A further object is to provide a method and apparatus for thermally stimulating and producing a well aligned substantially horizontally within a formation which contains a relatively viscous hydrocarbon. A still further object is to provide a method and apparatus for the continuous production of viscous hydrocarbon fluids from a single well disposed substantially horizontally through a bitumen holding formation.